This invention relates to initiation of a fluidized bed process for oxychlorination of methane, methyl chloride, other chlorinated derivatives of methane such as methylene chloride, chloroform and carbon tetrachloride and/or mixtures thereof by reaction with hydrogen chloride and air, in the presence of an oxychlorination catalyst. Catalysts of this type generally consist of one or more metallic chlorides supported on an appropriate support for use in a fluidized bed. For example, one such catalyst for oxychlorination of methane in a fluidized bed is disclosed in U.S. Pat. No. 3,657,367 of Robert J. Blake, et al.
The start-up of reactions and processes in general, and of oxychlorination processes in particular, is usually a carefully performed matter. It is necessary to introduce the feeds in a controlled manner so as to prevent formation of explosive mixtures, over-reaction, and other undesirable effects which may take place at start-up due to an imbalance of feed or insufficient control of operating conditions. For example, U.S. Pat. No. 3,585,246 of Vancamp, et al., discloses a process of initiating an oxygen-based oxychlorination reaction for hydrocarbons having from 1 to 4 carbon atoms and chlorinated derivatives thereof in which an inert gas or air is first introduced to fluidize the catalyst. Next, the chlorinating agent is admitted to the system in a quantity representing one-half of that normally employed during the oxychlorination reaction. Once the chlorinating agent and the air have had an opportunity to thoroughly mix, the material to be chlorinated is introduced. The bed temperature is then raised to the optimum temperature for the reaction, the air feed is cut out altogether and an oxygen feed gradually introduced until the temperature of the bed has reached the optimum value. As pointed out in the patent, care must be taken to bring the bed temperature up to a temperature at which the particular hydrocarbon being fed will react with the chlorinating agent and maintain this temperature through the initial phase of start-up, otherwise the reaction will die. It is also pointed out that other deviations from the procedure could result in excessive pressure build-up during start-up and may even result in an explosion.
In general, however, there is a risk posed by starting up a methane oxychlorination process by a procedure in which air is introduced before the introduction of the hydrocarbon feed. Such operation results in the environment inside the reactor first consisting of an oxidizing atmosphere; which is then converted to a reducing atmosphere as the hydrocarbon is charged. Passing from an oxidizing atmosphere to a reducing atmosphere increases the risk of formation of a flammable mixture of gases in the reactor. In the process of U.S. Pat. No. 3,585,246 this risk is decreased by introducing the feed directly into the fluidized bed rather than through a wind chest; however, there is still a danger of forming an explosive mixture in the free space above the bed if a quenching of the reaction should occur after both air and hydrocarbon feeds are switched on.
It is an object of the present invention to provide a process for initiation of a reaction comprising oxychlorination of a material to be chlorinated selected from the group consisting of methane, methyl chloride, chlorinated derivatives of methane and mixtures thereof with hydrogen chloride and air.
It is a further object of the present invention to provide a method for initiating such an oxychlorination reaction in which the danger of forming an explosive mixture can be lessened.
Another object of the present invention is to provide a method of initiating such an oxychlorination reaction which permits good control of the start-up procedure.
A further object of the present invention is to provide a method of initiating such an oxychlorination reaction in which the start-up can be conducted at a temperature initially below that required for the conduct of the oxychlorination process itself.